Medicine is dysgenic - I would be dead a few times over without modern treatments for asthma, which runs in my family. My children now have the opportunity to be born with the same bad genes that otherwise would have been selected out of the gene pool. Cumulatively over time, genetic fitness will decline to the minimum level needed for survivability in the environment. Medicine makes the environment much more survivable. Not to mention the more recent habits of agriculture and enough wide-spread cooperation that our tribes aren't constantly murdering eachother. (arguably)
The interesting case, is that our long-term survival is now more a question of information, culture, and knowledge than it is of our biological capacities. Our most interesting evolution is happening in the rapid and ephemeral'software' of shared knowledge and technology, and not the fleshy hardware ruled by genes.
So a gene goes from a huge handicap to a small handicap. That's not ruining the gene pool. Medicine doesn't even remove the selection pressure, let alone apply pressure in the wrong direction.
And you're probably wrong about saying you'd be dead; why did your ancestors survive it?
I wouldn't say that it has an acute immediate negative effect the gene pool by any measure, but it does certainly have an effect on the slow stochastic process shaping the gene pool. It would make intuitive sense that preventable, fecundity decreasing maladies will increase in frequency over time over many generations. Maybe that's not so much a pejorative effect as a beneficial adaptation to a new, more forgiving environment, if you look at it from the right perspective. Still I think that most people would agree that robust health in a low-tech environment is a nice trait to have in a population. Still, we're arguably pretty irreversibly reliant on fire and cooking.
Cave dwelling fish don't lose their eyes because of any immediate selection counter pressure, but from the slow reversion to the mean from no pressure either way. Or maybe the small pressure of nutrients spent on maintaining a useless organ.
Perhaps my example of my own case was misguided - I was turning blue and rushed to the emergency room as an infant, though. It was a single case provided to demonstrate a point where no single case matters that much.
The interesting case, is that our long-term survival is now more a question of information, culture, and knowledge than it is of our biological capacities. Our most interesting evolution is happening in the rapid and ephemeral'software' of shared knowledge and technology, and not the fleshy hardware ruled by genes.